Power scaling of resonantly pumped Yb-free Er-doped fiber laser

Abstract

Even though Yb-doped fiber lasers are known to be the most powerful and most efficient among all fiber lasers, recent successes in the eye-safe ~1.5μm Yb-Er-doped fiber lasers (where Er is excited through Yb-Er energy transfer) are quite impressive. Output power of Yb-Er fiber lasers reached ~300 W level and their optical-to-optical efficiency, for somewhat lower power levels, is exceeding 40% [2]. Nevertheless, as far as real eye safety is concerned, multi-hundred Watt Yb-Er fiber lasers typically carry in their output a significant fraction of competing 1-μm Yb emission, which totally compromises an eye-safe side of the application. Ultimate efficiency and thermal management of Yb-Er approach are also suffering due to: (i), inefficiency of Yb-Er energy transfer and, (ii), gigantic ~40% quantum defect of Er-doped fiber pumped at 9XX-nm. Presented here are very recent and successful results on power scaling of resonantly pumped Yb-free Er-doped fiber lasers and amplifiers. We are reporting an Ybfree Er-doped cladding-pumped fiber power scaling to ~50 W with ~57% optical-tooptical efficiency [6] in a few first experimental steps. This is clear manifestation of scaling potential of this most efficient approach to high power eye-safe fiber laser. The only competing approach to scalable eye-safe fiber laser implements Tm³⁺-doped fibers pumped at ~790 nm while relying on well known "2-for-1" process leading to quite efficient excitation of the ~2μm Tm³⁺ laser operation [4]. This approach has operational optical-to-optical efficiency quantum limit of ~75% [4], while resonantly pumped Ybfree Er-doped fiber laser's optical-to-optical efficiency quantum limit exceeds 95% due to its low-quantum-defect (QD) pump-lase scheme. Significant scaling potential of resonantly-pumped Yb-free Er-doped fiber lasers and amplifiers sets a path to an eye-safe fiber laser concept with drastically relaxed thermal management and nearly diffraction limited beam quality at ~kW-=-class power levels as well as high electrical to optical efficiency.